Top Angular 4 interview questions and answers

Explain component decorators in Angular4.

A decorator is the core concept when developing an angular framework with version 2 and above. It may become a core language feature for JavaScript soon. In angular 4, decorators are used extensively and are also used to compile a code. There are 4 different types of decorators:

Class decorators

Property decorators

Method decorators

Parameter decorators

A decorator is a function that is invoked with a prefixed “@” symbol and is immediately followed by a class, parameter, method, or property. A decorator returns the same thing which was given as an input but in an augmented form.

Write the CLI command to generate a component in Angular4.

Components are just simple classes which are declared as components with the help of component decorators. It becomes easy to create an application which already works, with the help of angular CLI commands. “Ng generate” is used to generate components, routes, services, and pipes. Simple test shells are also created with the help of this CLI command. For generating a component in angular4 with the help of CLI command, you need to follow the following syntax-

ng generate component component_name;

It generates the component and adds the component to module declarations.

Explain ngFor directive with an example.

The ngFor directive instantiates a template for every element of the given iterator. The different local variables of the ngFor directive can be used in iterations. The ngFor directive can even be used with the HTML elements. It also performs various changes in DOM. Several exported values can be aliased to local variables with the help of ngFor directive. It allows us to build data presentation lists and tables in our HTML templates. Here’s an example of ngFor directive with the help of HTML:

Explain property binding or one way binding in angular js.

Basically, property binding means passing data from the component class and setting the value of a given element in the view. It is a one-way binding in which the data is passed from component to the class. It allows us to control the element property values from component to class. Property binding in angular can take place by three ways:

Interpolation can be used to define a value, as long as the value being defined is a string.

Wrapping brackets around the element property and binding it to the component property is the most common type of property binding.

What do you understand by Isolated Unit Tests?

As the name implies, unit test is all about testing individual units of code. In order to answer some questions, isolating the unit of code under test is really important. When we do this, we are not forced into creating related pieces such as DOM elements for sorting. With the help of isolated unit tests, it becomes easier to implement everything. To simulate the requests, dependency injections are also provided. The individual sort function can be tested in isolation. And not only the sort function, any function can be tested in isolation.

What is a routing in angular js?

ngRoute module is used when you want to navigate through different pages of your application but you also want your application to be a single page application. This ngRoute module navigates through different pages of your application without reloading the entire application. The angular js route module should be included to make your application ready for routing. The ngRoute is added as a dependency in the application. The routing engine captures the specific URL requested by the user and renders the view based on the defined routing rules.

What do you understand by services with reference to angular js?

Services in angular js are used to organize and share code across your application. These are the suitable objects which are wired together with the help of dependency injection. The angular js services are lazily instantiated. The service is only instantiated by angular js only when the application component depends on it. In angular js, new services can be made or can even be used in other built-in services. Over 30 built-in services are present in angular js.